Satin white-clay compositions and methods of manufacture

ABSTRACT

A COATING PIGMENT COMPOSITION OF KAOLIN AND SATIN WHITE IS PROVIDED IN WHICH THE KAOLIN IS CLASSIFIED FROM NATURAL KALOLIN DEPOSITS TO A PARTICLE SIZE OF ABOUT 80% TO 96% BY WEIGHT LESS THAN 2U, ABOUT 55% TO 85% LESS THAN 1U, AND NO MORE THAN ABOUT 10% LESS THAN 0.2U, SAID SIZE VALUES BEING DETERMINED BY THE STANDARD CENTRIFUGAL-HYDROMETER METHOD.   D R A W I N G

Dec. 7, 1971 R. F. cbNLEY ET AL 3,625,725

SATIN WHITE-CLAY COMPOSITIONS AND METHODS OF MANUFACTURE Filed April 24.1969 mbga Kg wugg lUSOJSd M m mu m m a 9.9.22 5 3360 5 30:05am 2.2023MMO o No no v N m 9 8 0% m/ M 8 j M on /M T e 1 on 1 I M a M o cm H/ y00 Q O0.

United States Patent ()1 Eco 3,625,725 Patented Dec. 7, 1 971 3,625,725SATIN WHITE-CLAY COMPOSITIONS AND METHODS OF MANUFACTURE Robert F.Conley, Scotch Plains, and Mary Kate Lloyd, Westfield, .N.J., and BillyReid Catherwood, Macon, Ga., assignors to Georgia Kaolin Company FiledApr. 24, 1969, Ser. No. 818,877 Int. Cl. C09c 1/02 US. Cl. 106-306 6Claims ABSTRACT OF THE DISCLOSURE A coating pigment composition ofkaolin and satin white is provided in which the kaolin is classifiedfrom natural kaolin deposits to a particle size of about 80% to 96% byweight less than 2,u, about 55% to 85% less than 1,14, and no more thanabout 10% less than 0.2 said size values being determined by thestandard centrifugal-hydrometer method.

This invention relates to satin white-clay compositions and methods ofmanufacture and particularly to improvements in optical properties ofcoated paper by application of specific satin white-clay compositionsthereto. More specifically, this invention relates to an improvedcoating pigment used in the coating of paper and to the processing ofimproved satin white-clay pigments.

In the commercial operation of coating paper, dispersions of kaoliniteand adhesive, along with other pigments usually of high refractiveindex, are roll or blade coated onto a moving paper sheet and driedthereon. It has been observed that the presence of micro-voids in thedried coating improve certain optical properties, notably opacity andgloss, and to a lesser extent brightness and whiteness. One mode ofintroduction of controlled voids is by the use of certain acicularpigments in small concentrations. It has been theorized that suchpigments take up space by brush pile configuration and slowly releasewater during the drying process and thus introduce voids of a sizerelated to the particle length.

One such material is known in the trade as Satin White, a calciumsulfo-aluminate of somewhat indefinite composition, but believed to beprimarily Satin white, as now known in the trade, is produced by mixinga solution of calcium hydroxide with one of aluminum sulfate instoichiometric proportions. The chief problem in the manufacture ofsatin white is stabilityit must be kept in water suspension, usually atabout 25% solids. It is well recognized that drying satin white destroysit, together with the useful optical properties it imparts. It isobserved that the suspension is even degraded at temperatures above 75C. While 75% water may be higher than necessary for its stability, theextremely thixotropic viscosity of satin white in water makes itcompletely impactical to handle at solids much higher than 25%. The highWater content introduces several commercial problems. Shipping costs areexorbitant and shipping is prohibited where exposure to cold weatherresults. The latter problem arises because freezing of the water insatin white also destroys the pigmentary characteristics. The extrawater in satin white may dilute the coating composition and requireadditional drying time and costs for its removal.

We have previously found, as set forth in application Ser. No. 721,955,that premixing of satin white suspensions from the lime-alumprecipitation with kaolinites and spray drying thereafter yields apowdery material containing 5% or less moisture and whose coatingproperties are not degenerated as a result of drying. We have nowdiscovered that certain selected types of kaolinites when premixed withsatin white suspensions give even better optical properties. Theinvention is more clearly set forth in the following detailed examples.

EXAMPLE I A satin white composition is formulated by slurrying 5 partsof high purity lime in parts Water at room temperature and thoroughlymixing. A second solution of 25% aluminum sulfate is made up, a volumecorresponding to about an Al (SO -18H O/Ca(OH) weight ratio of 1.50. Thealuminum sulfate solution is added slowly (about 30 minutes total) tothe lime solution, so the temperature of the mixture does not rise aboveabout 32 C. The precipitation is continued until a pH of 11.9 isreached. Thereafter a starch suspension is added in an amountcorresponding to 10% by Weight of the precipitated calciumalumino-sulfate, or about 1.35 parts dry starch based on limeformulation. Starch acts as a binder in the finished coating formulationand its addition to satin white improves the rheology somewhat.

The precipitate is pressure filtered to 2526% solids. To 30 parts byweight of satin white solids is added 70 parts by weight of a broadparticle size kaolinite which had been previously acid flocced, filteredand dried and whose size distribution is given by curve A in FIG. 1. Thetotal solids were adjusted to about 35% by addition of 0.3% (totalsolids basis) of a dispersing chemical, sodium hexametaphosphate orsodium carbonate, in aqueous solution and the thin slurry spray dried ina Nichols Niro Utility spray drier (inlet temperature 280 (1., outlettemperature 135 (3.).

EXAMPLE II A formulation similar to Example I, except that the kaoliniteparticle size was very coarse, designated by curve B in FIG. 1, wasspray dried.

EXAMPLE III A formulaion similar to Example I, except that a fineparticle size kaolinite was employed, designated by curve C in FIG. 1,was spray dried.

EXAMPLE 'IV A formulation similar to Example I, except that a kaolinitewas employed whose particle size was slightly finer than that in ExampleIII, designated by curve D in FIG. 1, was spray dried.

EXAMPLE V A formulation similar to Example I, except that the solidscomposition was an 20 kaolinite-satin white ratio, was spray dried.

EXAMPLE VI A formulation similar to Example II, except the solidscomposition was an 80-20 kaoliniteasatin white ratio, was spray dried.

EXAMPLE VII A formulation similar to Example III, except the solidscomposition was an 80-20 kaolinite-satin white ratio, was spray dried.

EXAMPLE VIII \A formulation similar to Example IV, except the solidscomposition was an 80-20 kaolinite-satin white ratio, was spray dried.

The dry formulations from Examples I-VIII were made into standard starchcoating compositions and coated onto standardized paper rawstock sheet.The rheological and optical properties are set forth in Tables I and II.

It is apparent that kaolinite D, the finest particle size clay used,gave the best optical properties as well as the highest rheologicalvalues. The optical properties are desirable but the high rheologicalvalues are not.

Clays A through D are naturally occurring kaolins which have beenbleached to remove iron and separated into their respective particlesize fractions by commercial centrifuges. However, particle finenessshould not be construed as an exclusive criterion for the kaolinitecomponent in the pigment mixture. As seen from FIG. 1, the brightness(reflectance at 457 mp) trend of the dry kaolinite precursor parallelsthose of the spray dried composite. However, gloss and opacity, whichlikewise have parallel trends, are due more directly to particlefineness of the kaolinite than to those optical properties mentioned.Rheology, particularly at low shear (Brookfield 10 r.p.m.), shows apronounced improvement with large particle size kaolinite, the trendagain following particle size.

4 EXAMPLE XII A composition similar to Example IX but containing 100%clay E as pigment was processed as set forth in Example IX.

Specimens from Examples IX, XI, and XII were coated onto a standardizedpaper rawstock, specimen XI corresponding to previous specimen 4. Therheological and optical properties are set forth in Tables III and IV.

TABLE III Brookfield viscosity,

cp. at- Pigment Percent Specimen composition solids pH 10 r.p.m 100 r.pm

70 E-BO S 40. 2 9. 5 2, 880 648 80 E-2O S 39. 7 9. 4 72 344 70 D-30 S40. 1 9. 4 3, 920 784 100 E 44. 7 7. O 720 184 TABLE IV Reflec- Reflec-75 7 tance tance 1 whiteness Whiteness 1 Percent gloss gloss 1 at 457 myat 457 1111!. index index opacity 1 Calendered 2 nips at p.s.i.g.

TABLE I Specimens 9 and 10 exhibit the superior optical properties asobserved with specimen 11 (see #4 also) and Brookficcld y. markedimprovement in gloss and whiteness over the pure Pigment Percent il clayE, which itself is noted for superior optical properties Specimencomposition solids pH 10 r.p.m. 100 r.p.m. over clays A, B, C, and DHowever, rheologically, speci- 7011- s 38.4 9, 1,520 512 men 10 is muchsuperior to specimen 11 and approaches Z8 5332 3'3 2 328 Egg 35 a purekaolin, known and employed for its low coating 70 D-30 s 38:0 917 21 584viscosity. Inasmuch as coating rheology is profoundly 38 %:gg% 3'; gigaffected by the cooking of the starch binder, only mem- 80 0-20 8 38:3919 1,2 295 bers within a set, e.g., #l-8 or #942, can be compared8013-208 L120 432 40 (where a common cook is employed) and not cross-setmembers.

TABLE II Coat Reflec- Refiec- White- Whitewelght 75 75 tance at tance atness 1 ness Percent Percent Specimen lb./rm gloss gloss 1 457 In 457 myindex index opacity 3 opacity 1 1 Calendered 2 nips at 5 p.s.i.g. 2Reflectance difference, 700 mw400 my. 5 Reflectance difierence at 530 mover white/black.

A composition containing 70% clay E and 30% satin white was formulatedas in previous examples and coated onto standardized paper rawstock.

EXAMPLE X A composition containing 80% clay E and 20% satin white wasprocessed as set forth in Example IX.

EXAMPLE XI' A composition containing 70% clay D and 30% satin white wasprocessed as set forth in Example IX.

' It is an interesting anomaly that very large, thin platelets, as occurin clay E, give equal to or superior results to a clay whose diameter isquite small and whose particles have a thicker aspect ratio. Particlepacking would appear to be involved.

Another series of clay-satin white mixtures were formulated using thedelaminated clay E essentially void of particles 0.2 m and a fine, highquality undelaminated clay whose particle size is designated by curve F.

EXAMPLE XHI A composition containing 70% clay E and 30% satin white wasformulated, processed, and coated onto standardized paper sheet bytechniques set forth in previous examples; specimen 13 roughlycorresponds to specimen 9.

EXAMPLE XIV A composition containing 63% clay E, 7% clay F (-10 claymixture), and 30% satin white was formulated and processed as in Example13.

EXAMPLE XV A composition containing 56% clay E, 14% clay F (80-20 claymixture), and 30% satin White was formulated and processed as in Example13.

EXAMPLE XVI A composition similar to Example 13, but containing 80% clayE and 20% satin white.

clay and satin white deteriorates the rheology of the coatingformulation slightly and the optical properties of the coated papersignificantly. Thus in processing kaolin and satin white for a coatingpigment, it is advantageous to remove the fine kaolin fraction beforecombination and subsequent drying.

in addition to improving the quality of the product, removal of the finekaolin fraction is beneficial to the processing. Specimens equivalent incomposition to those cited in Examples 13, 14, 15, and 16 wereformulated with 0.3% dispersing agent only. In place of spray dryingthese immediately, their viscosity as a function of aging time wasmeasured and appears in Table VII.

l 25% solids, 0.1% Na2COa+0.2% (NaPOa)a added.

EXAMPLE XVIII A composition similar to Example 14, but containing 72%clay E, 8% clay F (90-10 clay mixture), and 20% satin white.

EXAMPLE XIX A composition similar to Example 13, but containing 100%clay E as pigment.

EXAMPLE XXH A composition similar to Example 13, but containing 100%clay F as pigment.

Specimens from Examples 13 through 22 were coated onto a standardizedpaper rawstock. The rheological and optical properties are listed inTables V and VI.

It is apparent that the presence of the fine particle size kaolin in thedelaminated kaolin-satin white system increases the viscosity in someinstances nearly As this mixture is a spray drying composition, the rateto the dryer is significantly reduced by the increase in viscosity.Reformulation after spray drying gives essentially the same viscositiesand trends as are observed in Table VII, thus confirming the coatingviscosity data in Table V.

Because of the limited solubility of calcium hydroxide, satin white isbest precipitated under chemical conditions wherein about 10-11% satinwhite solids results. Commercial practice has been to pressure filterthis dilute suspension to about 25%, the practical limit.

In spray drying the satin white-kaolin composite, two choices areavailable; (1) a 10% satin white slurry can be used with kaolin whichyields an easily pumpable slurry composite, but with more water to dry;or (2) a 25% satin white slurry may be used for the composite withdecreased Water content, but more viscous rheology and lower pumpingrate. Choice (1) circumvents a filtration step. The economics tend to beabout equal for both alternatives. However, the rheological propertiesof the products differ decidely as shown with Examples 23-30 and thedata in Tables VIII and IX.

TABLE V 1 Bmokfield EXAMPLE XXIII viscosity, cp. at 50 S l t tg H 10 Drykaolln A was blunged with a precipitated satm pemmen S p white slurrycontaining 10.5% satin white solids so that 33- 8-3 1 32% g; a pigmentratio of 80% kaolin-20% satin white re- 13 1 400 552 sulted at 38% totalsolids. The mixture was spray dried as ggag in Example 1, formulatedinto a standard coating compo- 1 600 324 sition and paper coated as setforth in previous examples. 37.7 10.1 gigs 7.2 10.1- 0 47.8 7.5 960 224EXAMPLE XXIV 45.4 7.3 1,880 344 Dry kaolin A was blunged with aprecipitated and pres- TABLE VI Coat Reflec- Refiec- White- White-Weight, 75 tance tance ness ness 1 Percent Percent Specimen lb./rm.gloss gloss l at 457 mp at 457 my index index opacity opacity 1 lCalendered 2 nlps at 5 p.s.i.g.

The data in Tables V and VI indicate the presence of fine particle sizeclay in a composite of delaminated sure filtered slurry of the satinwhite in Example 23 which contained 25 satin white solids afterfiltering, the composite containing 80% kaolin-20% satin white at 38%total solids and treated subsequently as in Example 23.

EXAMPLE XXV Dry kaolin A was processed in the same manner as in 8classified kaolin and satin white which may be made up into aqueouscoating compositions comprising an effective amount of each of satinwhite and kaolin in which the kaolin is classified from natural kaolindeposits to a particle size of about 80% to 96% by weight less than 2 pe 23 o P the plgmont who w 7 kaolmmicrons and about 55% to 85% less than1 micron, but 30% satin wh1te., no more than about less than 0.2 micron,said size EXAMPLE XXVI values being determined by the standardcentrifugalhydrometer method. D kaollll A was PFQCQSSEd In manner Setforfh 1 1 2. A dried particulate coating pigment composition of ExamPleexcept the Plgment ratlo was 70% kaohn' classified kaolin and satinWhite which may be made up 30% Satm Whlteinto aqueous coatingcompositions comprising an effec E A LE XXVII tive amount of each ofsatin white and kaolin in which D k h f h the kaolin is particle sizeclassified from natural kaolin 2 Was processed m t e manner set ondeposits and measures about 96% by weight less than m Xamp e 2 micronsand 85% less than 1 micron, but no more EXAMPLE XXVIII than about lessthan 0.2 micron, said analysis being Dry kaolin E was processed in themanner set forth gg gga by the Standard cenmfugal-hydrometer m Examp 1e20 3. A coating pigment composition as in claim 1 in EXAMPLE XXIX whichthe satin white content is present in an effective Dry kaolin E wasprocessed in the manner set forth amount to retain the effectiveness ofthe satin white as in Example 25. a paper coating pigment on rewettingafter drying but is not greater than about 30%. EXAMPLE XXX 25 4. A spradried coating pigment composition as in o y I s 5 Dry kaolin E wasprocessed in the manner set forth clalm 1 Wheretheatmwh1te1abollt inExample 5. A dried particulate coating pigment composition of TABLE VIIIclassified kaolin and satin white which may be made up into aqueouscoating compositions comprising satin white Brookfioliviscosity. 30 andkaolin in which the kaolin is a mechanically de- Pigment Percent ii.laminted material which is further particle size classified p ncomposition s ds p 10 -p- 100 -P- to yield about 80% by weight less than2 microns, about 23 so A-QOS 7,, 460 496 230 55% less than 1 micron andno more than about 10% 24 80 A403 25 320 216 less than 0.2 micron, saidanalysis being performed by 32" "'1 38238 2 2523331 iii 8:? '233 $.33 35the standard centrifugual-hydrometer method. 27 80 1,240 336 6. Acoating pigment composition as in claim 5 in I 38 12 3;; 5328?, 228which the satin white content is present in an effective 30 7013-3031,400 amount to retain the effectiveness of the satin white as 31 100A54.5 6.9 3,160 636 32 100 E 54. 7 7.0 7,680 1, 220 a paper coatmgplgment on rewettmg after drying but not 40 greater than about 30% TABLEIX Coat Refiec- Reflec- White- Whiteweight, 75 75 tance tance 1 nessness 1 Percent Percent Specimen lb./rm. gloss gloss at 457 m at, 457 myindex index opacity opaeity I Calendered 2 nips at 5 p.s.i.g.

With clays A and E there is little advantage in the use- ReferencesCited of either 10% or 25% satin white suspension as spray dryer feed onthe basis of optical properties. There is UNITED STATES PATENTS anadvantage rheologically, as the coating formulations 1, 07,773 2/1922Ryan l06-2l4 show a decreased viscosity when the 25% solids satin 35,6002/ 1948 Rafton l06--306 white is employed in the composite spray dryerfeed. In 42,671,032 3/ 1954 Thompson 06 most optical and rheologicalproperties the pre-filtered 3,063,354 11/1962 CIaXtO 106-214 X 25 satinwhite shows a distinct advantage over the pure 3,0 6,035 11/1962 Albert106214 X clay component. 3,075,710 1/ 1963 Fold et al. 24l-16 While wehave illustrated and described certain pre- 3,085,894 4/ 1963 Rowland106-306 ferred embodiments and practices of our invention, it will beunderstood that the invention may be otherwise em- LORENZO HAYES:Prlmary Exammel' b d'ed w'th' th c0 of the followin claims.

1 1 m e 5 g U.S. c1. X.R.

We claim:

1. A dried particulate coating pigment composition of 7 106-214; 117156UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No DatedDecember 7,

Inventor(s) Robggt F. fibril-MI It is certified that error appears inthe above-identified patent and that said Letters Patent are herebycorrected as shown below:

Column 2, line 33, "280" should read 380 line &1, under the headingEXAMPLE III, "formulaion" should read formulation Column 6, line 46,"deoidely" should read decidedly Signed and sealed this 21th day ofOctober 1972.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GO'I'TSCHALK Attesting Officer Commissionerof Patents JRM 90-1050 (10-69) USCOMM-DC wave-poo Q U S GDVIRNMINYPRINTING OFFICE: I. D SBfl-3J.

